Yulia Tymoshenko, Ukraine's former prime minister, has been sentenced to seven years in prison.
A judge ruled on Tuesday that the former leader of the Orange Revolution had exceeded her authority in 2009 when she negotiated a gas deal with Russia in 2009. Many Ukrainians believed the deal disadvantaged their country.
During her trial this week, Tymoshenko was led through a jeering crowd under a heavy police escort, as protesters shouted "Shame! Shame!" at her. There were minor clashes between the riot police and the crowd.
Western leaders criticised the move, with Catherine Ashton, the EU foreign policy chief, saying the prosecution was politically-motivated.
British Foreign Secretary William Hague said that the trial was "subject to numerous and serious violations of fundamental legal principles, in direct contradiction of common European values". He added that it could post a "major obstacle" to the Ukraine's interest in a Free Trade Agreement with the EU.
The Russians were also anxious about the ruling. Vladimir Putin, the Russian Prime Minister who signed the gas deal with Tymoshenko two years ago, said that he also did not understand her imprisonment. Russia's foreign ministry also commented that the trial had a "clear anti-Russian subtext".
Tymoshenko was once the heroine of the pro-Western Orange Revolution of 2004, which saw her rise to power. But she was forced into opposition in 2010.
The judge said the former leader would also have to pay back 1.5 billion hrivnas, around £119 million, lost by the state gas company as a result of the deal with Russia. Tymoshenko denies any wrongdoing and says that she will be taking her case to the European Court of Human Rights.